1. Field of the Invention
When a solid body is subjected to cyclic loading it undergoes a cyclic variation in temperature. The variation in temperature is a function of the variation in the sum of the principal stress or strain experienced by the body. The temperature changes can be measured using a sensitive infra-red detector.
2. Descriptions of the Prior Art
Two measuring systems are commercially available; one, SPATE (Trade Mark) uses a scanning device to assemble a full-field picture during a large number of cycles. The second and more modem device, DELTATHERM (Trade Mark) uses an array of diodes to record a full-field image during a small number of cycles. It is recommended that a black coating is used on the component with both devices. The primary reason for the use of the coating is to provide a surface of uniform emissivity, and the use of black converts the component into a `black body` thus maximising the emitted infra-red signal. The coating in common use by thermoelasticians is a spray-on black paint.